The conventional methods of adjusting the speed of stepping motor are as follows:
I. speed regulation of commutator motor
Advantages: ① it has simple structure of AC synchronous motor and good speed regulation performance of DC motor; ② it uses power supply voltage at low speed and step motor back EMF at high speed for natural commutation and reliable operation; ③ it has no additional slip loss and high efficiency and is suitable for starting and speed regulation of high-speed large capacity synchronous motor. Disadvantages: the overload capacity is low, and the capacity of the original motor cannot be fully developed.
II. Stator voltage regulation and speed regulation
Advantages: ① the circuit is simple, the device volume is small, and the price is cheap; ② the use and maintenance are convenient. Disadvantages: ① increase the slip loss in the process of speed regulation, which causes the rotor to heat up and has low efficiency; ② the speed regulation range is relatively small; ③ high slip motor is required, such as the specially designed torque motor, so its characteristics are relatively soft, which is generally applicable to asynchronous motor under 55kW.
III. rotor series resistance speed regulation
Advantages: ① low technical requirements, easy to master; ② low equipment cost; ③ no electromagnetic harmonic interference. Disadvantages: ① the series cast iron resistance can only be used for step speed regulation. If the liquid resistance is used for stepless speed regulation, the maintenance requirements are high; ② the additional slip power in the process of speed regulation is all converted into the loss of the heating form of the series resistance, with low efficiency. ③ the speed regulation range is not large.
IV. speed regulation of electromagnetic slip clutch
Advantages: ① simple structure, small control device capacity and low value; ② reliable operation and easy maintenance; ③ no harmonic interference. Disadvantages: ① the speed loss is large, because the electromagnetic slip clutch itself has a large slip, so the maximum speed of the output shaft is only 80% - 90% of the synchronous speed of the motor; ② in the process of speed regulation, the power of the transfer difference is all converted into the loss in the form of heat energy, with low efficiency.